The Chapters raised during this Founding consisted entirely of Primaris Space Marines who had been created from a new stock of modified gene-seed -- crafted over ten millennia by Archmagos Dominus Belisarius Cawl -- as the supreme contingency plan and the ultimate defenders of the Imperium of Man against the darkness that now encroaches from all sides.
The Ultramarines Primarch Roboute Guilliman, always an optimist, but never a fool, had learned from the mistakes of the Horus Heresy. He had foreseen that the forces of Chaos would never relent in their aim to bring the Imperium of Man low.
Therefore, he set a task for the Priesthood of Mars: to develop a new legion of transhuman warriors -- the Primaris Space Marines -- who were bigger, more physically powerful and possessed faster reaction times than their original Astartes counterparts.
Developed by Archmagos Dominus Cawl on orders from Guilliman 100 standard centuries past, the Primaris Space Marines were perfected by the Mechanicus during the long intervening millennia.
Now, as the Imperium is poised on the brink of annihilation at the hands of its myriad foes, Guilliman's task is at last complete.
In the latter years of the 41st Millennium, the scattered Space Marine Chapters of the galaxy have been bled dry by ten thousand standard years of constant battle. With the advent of gigantic Warp Storms that swallow whole star systems, the formation of the Great Rift and constant attacks by the forces of Chaos, rampaging xenos and more, the Adeptus Astartes are stretched thinner than ever.
With many Chapter planets now actively under siege, some Chapters are confirmed as destroyed or lost, and even those faring relatively well have suffered high casualties and are in desperate need of reinforcement.
With the resurrection of the Primarch Roboute Guilliman, the Avenging Son has assumed command as lord commander of the Imperium over all of Humanity's military forces. Finally, after ten millennia, he has put into action his ultimate contingency plan -- the Primaris Space Marines.
These new warriors are the next step in the evolution of the Emperor's original Angels of Death, genetically altered from their brethren to be bigger, stronger and faster. The Primaris Space Marines represent timely reinforcements for the Imperium's armies as their enemies close in for the kill.
This initial wave of Primaris Space Marines emerged from over 10,000 standard years of stasis fully psychologically indoctrinated to each fulfil a single strategic role. Some were Intercessors, some Aggressors and so forth, and almost all specialised only in that one area of combat.
These warriors were able to immediately take up their front-line combat duties with the expertise of veterans, and all possessed a modicum of additional skill with Machine Spirits thanks to their Martian heritage.
Yet ultimately they were somewhat strategically inflexible, for they had not undergone the gruelling progression through their existing Chapters' companies or gained the wealth of experience that progress bestowed. Some of these Martian Primaris Marines formed entirely new Chapters such as the Rift Stalkers or the Silver Templars.
The rest joined the Indomitus Crusade as "Greyshields," fighting together with the scions of other Chapters and Primarchs as part of the force known as the Unnumbered Sons until the Indomitus Crusade fleets reached their adoptive homeworld or the fleet of the Firstborn Chapters they were destined to join.
Each time such a momentous occasion came, another cadre of Battle-Brothers would peel off and reinforce the Chapter whose colours they wore and whose genetic heritage they shared. Not all of these Primaris reinforcements had an easy time integrating with their erstwhile Firstborn brothers, but ultimately all brought fresh strength to the Space Marine Chapters fighting furiously against the tide of horrors vomited from the Great Rift.
The newly reinstated Lord Commander of the Imperium has decreed that those Chapters most devastated by the ongoing wars should be amongst the first to be reinforced with this new breed of transhuman warrior. Starting with the Ultramarines, but also deploying these new Space Marines to every other Chapter in need, Guilliman aims to reinforce the Imperium's scattered defenders across the galaxy. It is not just as reinforcements to existing Chapters though.
Guilliman has also ordered the creation of a host of new Chapters, the so-called "Ultima Founding," composed entirely of Primaris Space Marines. The warriors of these new Chapters were created entirely using the new processes discovered by Archmagos Belisarius Cawl and established with all the necessary weapons, armour and equipment that they will need to conduct their defence of the Imperium.
These Chapters still trace their genetic lineage back to the gene-seed of the First Founding, and scions of all nine Loyalist Space Marine Legions emerged from the vaults beneath the Red Planet. They benefit from three additional gene-seed organs and larger size, but it still remains to be seen if Cawl was able to successfully stabilise any of the known genetic deviations or impart any additional resistance to the effects of Chaos.
Many of these new Chapters have been assigned homeworlds on the edge of the Great Rift, the Imperium's new frontline in the war against Chaos, though some have inherited the empty fortress-monasteries of Chapters that had been lost to the attrition of constant war. Many of these worlds face a continuous battle against the daemons of the Warp, as well as an unpredictable mix of xenos raiders, pirates and invaders.
"We have fought the Long War against Chaos without them for ten thousand years. New genetics? New weapons? Spawned from the work of a tech-magos trying to imitate - no, worse - to improve upon the Emperor's own labours? Battle-Brothers who do not even serve time in the Scout Companies or the Devastators before taking their place in the line? I neither trust nor need such warrriors within my ranks Pavras. Dorn's Fist, they aren't even proven in battle!"
At the dawn of the Indomitus Crusade to retake the Imperium from the advancing armies of Chaos and xenos alike, Lord Commander of the Imperium Roboute Guilliman gathered his new armada, along with elements of the Adeptus Custodes, a small contingent of the Silent Sisterhood and a vast war host of Primaris Space Marines as he fought to liberate the scattered bastions of the Imperium.
Some, Guilliman had forged into new Space Marine Chapters, whole brotherhoods comprised only of these new transhuman warriors. Others he offered to the existing Space Marine Chapters. Many Chapter Masters welcomed their Primaris brethren into their ranks, accepting the new reinforcements gladly.
Others, though, viewed these new creations with suspicion or outright hostility, claiming that the Emperor's work should never have been meddled with by mere mortals.
Fortunately, the Emissaries Imperatus, a Shield Host of the Adeptus Custodes, the elite bodyguard of the Master of Mankind, stepped forward to intercede, stating that the gift that was the Primaris Marines was the will of the Emperor.
As "Heralds of the Golden Throne," they accompanied Guilliman's crusade, many of them taking to the air as Vertus Praetors, the quicker to deliver messages of reinforcement to the embattled Space Marines.
The presence of the Adeptus Custodes also ensured that even the most traditional Chapters accepted the Primaris warriors into their ranks. One does not decline a gift from the Emperor's own hand, after all.
As the Indomitus Crusade launched by Guilliman penetrated deeper into the galaxy, Archmagos Cawl kept his automaton workers on overdrive, risking meltdowns with their accelerated speeds.
Locked deep in the labyrinthine holds of his Ark Mechanicus Zar-Quaesitor, thousands of Primaris Space Marines -- some comprising entirely new Chapters and others designated as reinforcements for existing ones -- were awakened out of stasis and made ready to join the fray.
After the fighting was done, the Crimson Fists marvelled at the return of Roboute Guilliman, but were even more grateful for the arrival of Primaris Space Marines bearing their own heraldry. Here were warriors whose genetic composition was closer to their own primarch, Rogal Dorn, than had ever before existed.
For his raw material, Cawl had selected warriors of Terra, and had taken them only a few generations after the original Imperial Fists had been created by the Emperor. Indeed, some had been held in stasis since the days of the Great Crusade; a few of the Primaris Space Marines could recall having seen Rogal Dorn himself.
Again and again the crusaders watched the same tale unfold. When those of the Ultima Founding were brought before their Chapters, it was like a meeting of brothers separated at birth. Arriving at a time of great darkness and upheaval, the new transhuman warriors' strength was welcomed.
Such unusual reunions were repeated on many Astartes worlds, including Chogoris, Ultramar and Baal, where the Crusade arrived even as the proud Sons of Sanguinius were making what they thought would be their last stand against the Tyranids of Hive Fleet Leviathan during what became known as the Devastation of Baal.
Despite cleaving a wide path through the darkness that beset the Imperium, the Indomitus Crusade began to break down. When the vast holds of the Zar-Quaesitor were at last emptied, Archmagos Cawl departed, for he had many more secret vaults to activate in order to complete the Ultima Founding.
Once deployed, the new Primaris Chapters -- such as the Rift Stalkers or the Umbral Knights -- remained after the initial conﬂicts were won, seeking to consolidate the Crusade's gains; in many cases, they did this by establishing their own new Chapter planets.
In this way, the Crusade not only freed worlds from the tyranny of the Dark Gods, but also strengthened their defences against further attacks that were sure to come. Finally, Roboute Guilliman could no longer delay responding to the distress signals coming from his Chapter's own home Realm of Ultramar, which was itself once more besieged.
All their triumphs were but a sliver of light piercing the ink-black void, their many campaigns unable to reach the vast number of imperilled planets -- yet it was a start. Later it was said that during the darkest hours the Imperium had endured since the Horus Heresy, it was the Indomitus Crusade -- and the reinforcements of the Ultima Founding -- that gave Mankind the hope to persevere.
Notable Ultima Founding Chapters
- Codex Adeptus Astartes - Dark Angels (8th Edition), pg. 19
- Codex Adeptus Astartes - Blood Angels (8th Edition), pg. 42
- Codex Adeptus Astartes - Space Marines (8th Edition), pp. 20-21, 30, 53
- Codex: Space Marines (9th Edition), pp. 8, 63, 71, 73
- Codex Heretic Astartes - Chaos Space Marines (8th Edition), "Pinnacles and Nadirs - The Primogenitor Primaris," pg. 48
- Codex: Imperial Knights (8th Edition), pg. 55
- Codex Supplement: Blood Angels (9th Edition), pp. 18-19, 31
- Codex Supplement: White Scars (8th Edition), pg. 7
- Codex: Tyranids (8th Edition), pg. 39
- Dark Imperium (8th Edition Starter Set), pg. 15
- Warhammer 40,000: Conquest 7, "Ultramarines: Successor Chapters"
- White Dwarf (October 2017), "Eavy Metal - Create your own Chapter", pp. 117-119
- Dark Imperium (Novel) by Guy Haley, Chs. 6, 15, 20
- Traitor by Deed (Novella) by Ben Counter, Ch. 1
- Warhammer 40,000 Community - The Ultima Founding
- Warhammer Community - New Warhammer 40,000: The Indomitus Crusade & the Dark Imperium
- Warhammer Community - A New Breed of Hero
- Warhammer Community - Successor Chapter Showcase: Paul Norton's Iron Ravens
- Warhammer Community - Successor Chapter Showcase: Martin Morrin's Black Vultures